Yeah, that sounds like a great idea. The earlier in the process developers will join such a group, the sooner they will get feedback about their ideas, maybe something similar had already been done that they can borrow ideas from or decide to join that project instead.

It could be as simple as a steemit.chat or discord channel where people can discuss their apps at first. That shouldn't be too hard to set up and find a handful of developers to get it started :)